San Francisco -LRB- CNN -RRB- -- The three largest U.S. cellular carriers by subscribers sell the latest iPhone , and next week , eighth-place C Spire Wireless will join the group .

Some people were taken aback this week when C Spire , which only has stores in Mississippi , Southwest Alabama and Southwest Tennessee , announced that it will begin carrying the iPhone 4 and 4S on November 11 .

Among those grumbling over the news were some of T-Mobile USA 's 33.6 million subscribers . How , they asked , could a regional carrier get the coveted product before one of the big four ?

C Spire 's infrastructure is based on a cell standard used by Verizon Wireless and Sprint Nextel , which now both have the iPhone , but it is not common in other countries . C Spire , formerly Cellular South , has a deal with Verizon so that customers who travel outside of its Mississippi home base can still make calls .

Since C Spire 's network uses the same underpinnings and antenna bands as Verizon , Apple did not have to make modifications to its phones beyond what it already did for Verizon when it launched there in February . An Apple spokeswoman confirmed that C Spire would begin selling the phone next week , but she did not respond to a question about whether the company needed to modify the hardware .

The iPhone 4S , Apple 's newest gadget , uses a special antenna receiver from Qualcomm that works on typically incompatible networks . `` IPhone 4S is now a world phone , so both GSM and CDMA customers can roam worldwide on GSM networks , '' Bob Mansfield , Apple 's head of hardware engineering , says in a promotional video .

T-Mobile 's network runs on the global standard called GSM . AT&T Mobility also uses GSM . That 's what makes T-Mobile an attractive takeover target for AT&T , which plans to bolster its own network using T-Mobile cell towers , as long as the merger is approved . -LRB- C Spire , along with Sprint , are suing to block the acquisition , saying it will reduce competition . -RRB-

While AT&T and T-Mobile use the same basic network infrastructure , their cell signals operate on different antenna bands . That prevents T-Mobile from easily making iPhones run on its network .

When asked why C Spire got the iPhone before T-Mobile , Brad Duea , a T-Mobile senior vice-president , smiled , having likely fielded the question before .

`` The iPhone already works with their bands , '' he said in an interview on Wednesday . `` They did n't have to change anything . ''

Since the original iPhone came out in 2007 , owners have been able to take the devices to T-Mobile , swap out a SIM card and use them on the network . But as Apple has added 3G and faster data speeds for AT&T , the unofficial T-Mobile iPhones -- more than a million in all , T-Mobile has said -- have not been able to exceed 2G speeds . AT&T 's and T-Mobile 's 3G and so-called 4G networks operate on different bands .

Another T-Mobile executive , Cole Brodman , recently addressed the issue publicly at a conference and in a letter to customers , though not in great deal . Executives say that , while they 'd like to have the iPhone , Android is a fine alternative to the iPhone .

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C Spire Wireless will be the fourth U.S. carrier to get the iPhone

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T-Mobile , the fourth-largest carrier , still has no plans to carry it

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C Spire operates on the same network bands as Verizon